Glow plug for diesel engine with ptc control element disposed in small-diameter sheath section and connected to the distal end thereof

Abstract

A glow plug for a diesel engine includes a heat generating coil, a control coil, a sheath, an electrode rod, and a housing. The heat generating coil serves as a heater element. The control coil is connected in series with the heat generating coil and serves as a controller for controlling power supply to the heat generating coil. The control coil has a positive temperature coefficient of resistance larger than that of the heat generating coil. The sheath accommodates the heat generating coil and the control coil to be embedded in a heat-resistant insulating powder. The sheath has an elongated small-diameter portion on a distal end side thereof and a large-diameter portion on a rear end side thereof. The heat generating coil is connected to an inner wall of a distal end of the small-diameter portion of the sheath. The electrode rod has a distal end portion to which one end of the control coil is connected. The housing supports a rear end portion of the sheath on the distal end side thereof, and the electrode rod. The heat generating coil is disposed in a distal end portion of the small-diameter portion of the sheath, and the control coil is disposed to extend from the small-diameter portion to the large-diameter portion of the sheath.

What is claimed is: 
     
       1. A glow plug for a diesel engine, comprising: a first helical resistor serving as a heater element;   a second helical resistor connected in series with said first helical resistor said second helical resistor having a positive temperature coefficient of resistance larger than that of said first helical resistor, and said second helical resistor controlling power supply to said first helical resistor;   a sheath enclosing said first and second helical resistors in a heat-resistant insulating powder, said sheath having an elongated small-diameter portion on a distal end side thereof and a large-diameter portion on a rear end side thereof, one end of said first helical resistor being connected to a distal end inner wall of said small-diameter portion of said sheath;   an electrode rod having a distal end portion to which one end of said second helical resistor is connected; and   a cylindrical housing for supporting said large-diameter portion on a rear end side of said sheath, and said electrode rod,   wherein said first helical resistor is disposed in a distal end portion of said small-diameter portion of said sheath, said second helical resistor is disposed from said small-diameter portion to said large-diameter portion of said sheath, and said second helical resistor is connected to said first helical resistor at the distal end side of said small-diameter portion.   
     
     
       2. A plug according to claim 1, wherein said second helical resistor has a small-diameter portion corresponding to a diameter of said small-diameter portion of said sheath and a large-diameter portion corresponding to a diameter of said large-diameter portion of said sheath, said small-diameter portion of said second helical resistor disposed in said small-diameter portion of said sheath together with said first helical resistor, and said large-diameter portion of said second helical resistor arranged in said large-diameter portion of said sheath. 
     
     
       3. A plug according to claim 2, wherein a rear end portion of said small-diameter portion of said second helical resistor is arranged on said rear end side of said sheath and includes a coupling portion between said small-diameter portion and said large-diameter portion of said sheath. 
     
     
       4. A plug according to claim 3, wherein said sheath has a taper portion at least partially defining said coupling portion. 
     
     
       5. A plug according to claim 1, wherein said second helical resistor has a taper coupling portion a small-diameter portion, and a large-diameter portion, wherein said taper coupling portion of said second helical resistor is at least partially defined between said small-diameter portion and said large-diameter portion of said second helical resistor, and said taper coupling portion of said second helical resistor has a winding pitch not less than that of said small-diameter and large-diameter portions of said second helical resistor. 
     
     
       6. A plug according to claim 1, further comprising a connecting portion for electrically connecting opposing helical end portions of said first and second helical resistors, and wherein said second helical resistor controls power supply to said first helical resistor through said connecting portion. 
     
     
       7. A plug according to claim 6, wherein said first and second helical resistors have connecting ends extending in one of a straight axial direction and an oblique direction at said opposing helical end portions thereof, and said connecting portion connects said first and second helical resistors at a predetermined gap by welding said connecting ends of said first and second helical resistors. 
     
     
       8. A plug according to claim 1, wherein said small-diameter portion of said sheath has a length not less than three times a diameter thereof. 
     
     
       9. A plug according to claim 8, wherein when said small-diameter portion of said sheath has a diameter of 3.5 mm, said small-diameter portion has a length of 12 to 40 mm. 
     
     
       10. A glow plug comprising: a sheath defined by a small-diameter distal portion and a large-diameter portion;   a first coil disposed entirely within said small-diameter distal portion of said sheath; and   a second coil, coupled to said first coil, said second coil having a first portion disposed in said large-diameter portion of said sheath, and a second portion extending into said small-diameter portion of said sheath.   
     
     
       11. The glow plug of claim 10, wherein said first coil is coupled at one end to an inner wall of said small-diameter distal portion of said sheath. 
     
     
       12. The glow plug of claim 10, further comprising: an electrode, coupled to said second coil, to provide power to said first coil.   
     
     
       13. The glow plug of claim 10, wherein said first and second coils are embedded in a heat-resistant insulating material. 
     
     
       14. A glow plug for a diesel engine, the glow plug comprising: a sheath having a first portion having a diameter and a cap end, a second portion having a diameter that is greater than the diameter of the first portion, and a tapered portion fixed to the first portion at a first coupling point and fixed to the second portion at a coupling point P;   a heating coil disposed within within the sheath first portion and electrically coupled to the cap end;   a control coil having a coupling portion disposed between a first control and a second control, the first control disposed at least within the sheath first portion and coupled at a first end to the heating coil, the first control having a second end coupled to the coupling portion adjacent to the coupling point P; and   a rod disposed within the sheath and coupled to the second control of the control coil.   
     
     
       15. The glow plug of claim 14, the sheath first portion having an axial length that is at least 3 times the diameter of the sheath first portion. 
     
     
       16. The glow plug of claim 15, the sheath first portion having an axial length that is at least 6 times the diameter of the sheath first portion. 
     
     
       17. The glow plug of claim 16, the sheath first portion having an axial length of 12 mm to 40 mm. 
     
     
       18. The glow plug of claim 14, further comprising: a housing disposed about the sheath, the housing having a seat end located a linear space from the coupling point P.   
     
     
       19. The glow plug of claim 14, the first control having a diameter that equals a heating coil diameter. 
     
     
       20. The glow plug of claim 14, the first control disposed within the sheath second portion. 
     
     
       21. The glow plug of claim 20, the first end of the first control extending on one of a straight axial direction and an oblique direction to the heating coil and welded to the heating coil to form a gap between the first control and the heating coil. 
     
     
       22. The glow plug of claim 14, the coupling portion having a variable diameter wherein the variable diameter of the coupling portion increases in steps from the first control to the second control. 
     
     
       23. The glow plug of claim 14, the coupling portion having a variable diameter wherein the variable diameter of the coupling portion is formed from a pitch that is at least equal to at least one of a pitch of the first control and a pitch of the second control. 
     
     
       24. The glow plug of claim 14, the coupling portion having a variable diameter wherein the variable diameter of the coupling portion is formed from a pitch that is greater than at least one of a pitch of the first control and a pitch of the second control. 
     
     
       25. The glow plug of claim 14, the second control having a diameter that is greater than the diameter of the first control. 
     
     
       26. The glow plug of claim 25, the second control having a pitch that is less than a pitch of the first control. 
     
     
       27. The glow plug of claim 14, the control coil formed from a continuous wire.